Sahih Muslim Book 3, Hadith Number 624.

Chapter : The quantity of water that is desirable for a bath because of sexual intercourse, bathing of the male and female with one vessel in the same condition and washing of one of them with the left-over of the other.

‘Aisha reported: The Messenger of Allah (may peace be upon him) washed himself with water from a vessel (measuring seven to eight seers) because of sexual intercourse.